The invention discloses a device and a method for tomography, especially single photon emission computed tomography (SPECT).
Single photon emission computed tomography is a method with associated devices for three-dimensional imaging of radio pharmaceuticals, which have been introduced into an object. Human beings or animals may be provided as the object. The radio pharmaceuticals introduced into the object emit photons or gamma quanta. These photons are registered and evaluated by the device. The position, that is to say, the spatial distribution of the radio pharmaceuticals, is obtained as the result of this evaluation. In turn, the position of the radio pharmaceuticals allows inferences to be made regarding the object, for example, regarding a distribution of tissue in the object.
One known device for the implementation of single photon emission computed tomography comprises a gamma camera and a collimator positioned in front of the camera. The collimator is generally a lead plate with a large number of channels passing in a perpendicular direction through the plate. The provision of these channels ensures that, on the one hand, only photons passing in a perpendicular direction are registered and, on the other hand, that a spatially resolved measurement is possible. The camera together with the collimator is moved around the object. As a result, a large quantity of positional data is gathered. These data are known as projection shots. The position of the radio pharmaceuticals within the object can be determined from the positional data obtained from around the object.
In order to screen scattered radiation originating from the photons, it is generally also necessary to gather energy data. The camera is therefore normally designed in such a manner that the energy of the falling photons can be determined at the same time.
Scattered radiation always provides a lower energy by comparison with the actual measured radiation. Accordingly, scattered radiation can be screened ignoring photons with low energy. Determining an upper limit for the energy of the photons may also be relevant for screening background radiation.
The methods and/or the devices described above already represent part of the general available technical knowledge, because methods and devices of this kind have been used for more than 30 years.
Single photon emission computed tomography (SPECT) and position emission tomography (PET) are instruments for the quantitative imaging of spatial radio tracer distributions in vivo. Alongside their use in human medicine, these methods can be used in pharmacological and pre-clinical research for the development and evaluation of innovative tracer compounds. Although various systems for the examination of small laboratory animals are already available in the context of PET, corresponding developments have not been made in the field of SPECT or have only been made to an inadequate extent; indeed, this is still the case although TC-99 m and I-123-marked radio pharmaceuticals have a disproportionately greater relevance than PET nuclides.
A high-resolution, high-sensitivity animal SPECT would provide the advantage for pre-clinical research of an animal-preserving method, which would allow dynamic and reproducible studies of an individual to be performed with reliably informative results. This advantage is favoured by the fact that, with the above named radio isotopes, extremely high specific activities can be achieved (a factor of approximately 100 by comparison with PET nuclides), which are indispensable for interference-free in vivo measurements (low mass dose). In this context, corresponding marking methods must still be developed.